Preparation and Fractionation of Rhizobium Bacteroids by Zone Sedimentation through Sucrose Gradients

Abstract

Zone sedimentation through sucrose gradients was used for preparing Rhizobium bacteroids from lupin [Lupinus angustifolius] nodules and for separating them into slowly and rapidly sedimenting fractions. The purity of the bacteroids was established by EM and by enzyme assays and they were shown to contain a CO-insensitive cytochrome c oxidase. Bacteroids sedimented more rapidly than broth-cultured Rhizobium bacteria, and bacteroids from old nodules sedimented more rapidly than bacteroids from young nodules. There appear to be at least 2 forms of bacteroid in old nodules: slowly sedimenting bacteroids with moderate colony-forming ability resembling the bacteroids found in young nodules, and rapidly sedimenting bacteroids with much lower colony-forming ability.